Powder coating spray systems are used to apply powder paints and coatings to a variety of products including, for example, appliances automotive components, furniture and storage shelving, electrical transformers, and recreational equipment. These systems often apply the coating materials to such products electrostatically by using one or more electrostatic spray devices in a spray booth enclosure setting. A powder feed system is used to supply the coating material to the spray devices and a powder recovery system is typically employed to capture over-sprayed powder material for re-use. The recovered powder coatings may be transferred to a collection bin for later re-use or disposal.
Known powder recovery systems, especially those employed in larger production-type powder coating spray booths using a plurality of spray application devices, often use cyclone separators and/or filter elements for collection of over-sprayed powder coating material. Such a powder coating spray system using cyclone separators is disclosed in International Application Number PCT/GB98/02569, owned in common by the assignee of the present invention, the entire disclosure of which is fully incorporated herein by reference.
Cyclone separators used in powder recovery systems have either been very large single or dual side by side cyclones, multicyclones, or pairs of such cyclones having tangential or axial feed inlets.
In cyclones of the vertical feed type, the air entrained over-spray powder is fed vertically downwards from a common inlet manifold into the separators and a circumferential velocity is imparted to the air-entrained powder coating material by veins. In addition to the inlets, which are typically located in the booth walls near the ceiling, and are useful for capturing air-entrained powder coating material, intakes are sometimes provided near the floor of the powder spray booth. In such cases, a vertical channel connects the intake to the inlet to the cyclone which is near the ceiling of the booth. Such intakes are useful for recovering powder coating material from the area near the floor of the booth.
Sweeper devices may be employed to move over-sprayed powder coating material which has collected on the floor to a recovery intake. The sweeper device may take the form of a scraper bar which may be magnetically coupled to a drive positioned externally of the powder booth, such as is disclosed in International Application Number PCT/GB98/02569. The advantage of this is that the drive mechanism is outside the booth and therefore not covered by powder, and therefore it does not need to be cleaned when changing powder color.
To maximize the amount of powder which settles on the floor of the booth and can, therefore, be collected at the floor level cyclone intakes by the sweeper device, the booth walls and ceiling, or the booth canopy, are preferably made from non-conductive material. For example, the booth canopy may be made from a plastic material. Alternative materials include stainless steel.
In vertical cyclones, the over-spray powder is separated from the air by the combined effect of centrifugal and gravitational forces and falls to the bottom of the separators to be collected and removed. The cleaned air is then typically directed vertically upwards through ducts, one per cyclone separator, which pass through the center of the cyclone and into an exhaust manifold. The air then passes through a further powder, or dust, recovery unit containing one or more filter elements to remove any fine powder particles still entrained in the air, before being exhausted to atmosphere.
The captured powder coating material may be collected below the cyclones in a collection bin or hopper, for disposal or re-use. In addition, a sieve member may be employed between the cyclone exhaust at the cyclone's open throat end and the collection bin. Known sieve members are typically of similar size to the circular exhaust end of the cyclone. Known transfer means to deliver the captured powder from the collection bin, or hopper, located below the cyclone to a more distant collection hopper whereby the collected powder can be dumped into a feed hopper, is through a series of at least two pinch valves. Alternatively, an improved transfer means, found in International Application Number PCT/GB98/02569, comprises a venturi pump in combination with a mini cyclone. The known improved combination requires far less sophisticated controls than the dual pinch valve setup. Both methods still require cleaning of all surfaces contacted by the powder coating between powder coating color changes.
Known powder feed systems include a powder pump, a powder hose connecting the pump to a spray application device, and a pick-up, or suction, tube. Of course, there may be a plurality of such components. The suction tube may be inserted directly into a feed hopper or a virgin powder box. It is known to place the box, or hopper, on a vibratory table to provide continuous movement of powder and help break up any agglomerates. When a plurality of pumps, suction tubes and powder spray devices are employed, output can vary between pumps and can randomly surge, affecting powder coating application quality.
In such systems, changing the powder type (e.g., powder paint color) generally requires the cleaning of all system components that have come in contact with the previously applied powder. This cleaning process is intended to avoid the contamination of the new powder by the previously used powder. However, the longer it takes for the cleaning process to complete, the longer the spray system is off-line. The cleaning process completion time is dependent on a number of factors including, for example, the number of spray system components, their internal and external geometries that may have come in contact with the previously applied powder coating, and the type of powder. Hence, if the spray system includes a larger number of components having complicated or irregular geometries, the longer it takes to clean the system and the longer the spray system is “off-line” or not working. Long off-line times are very undesirable because they cause a decrease in overall spray system productivity. Hence, apparatuses and methods that minimize the time required for changing powder colors in powder coating systems are highly desirable.